The invention relates to temperature changing devices and, in particular, to portable or disposable food or beverage coolers.
There are many foods and beverages that may be stored almost indefinitely at average ambient temperature of 20.degree.-25.degree.C. but that should be cooled immediately before consumption. In general, the cooling of these foods and beverages is accomplished by electrically-run refrigeration units. The use of these units to cool such foods and beverages is not always practical because refrigerators generally require a source of electricity, they are not usually portable, and they do not cool the food or beverage quickly.
An alternate method for providing a cooled material on demand is to use portable insulated containers. However, these containers function merely to maintain the previous temperature of the food or beverage placed inside them, or they require the use of ice cubes to provide the desired cooling effect. When used in conjunction with ice, insulated containers are much more bulky and heavy than the food or beverage. Moreover, in many locations, ice may not be readily available when the cooling action is required.
Ice cubes have also been used independently to cool food or beverages rapidly. However, utilization of ice independently for cooling is often undesirable because ice may be stored only for limited periods above 0.degree. C. Moreover, ice may not be available when the cooling action is desired.
In addition to food and beverage cooling, there are a number of other applications for which a portable cooling device is extremely desirable. These include medical applications, including cooling of tissues or organs; preparation of cold compresses and cryogenic destruction of tissues as part of surgical procedures; industrial applications, including production of cold water or other liquids upon demand; preservation of biological specimens; cooling of protective clothing; and cosmetic applications. A portable cooling apparatus could have widespread utility in all these areas.
Most attempts to build a self-contained miniaturized cooling device have depended on the use of a refrigerant liquid stored at a pressure above atmospheric pressure, so that the refrigerant vapor could be released directly to the atmosphere. Unfortunately, many available refrigerant liquids for such a system are either flammable, toxic, harmful to the environment, or exist in liquid form at such high pressures that they represent an explosion hazard in quantities suitable for the intended purpose. Conversely, other available refrigerant liquids acceptable for discharge into the atmosphere (such as carbon dioxide) have relatively low heat capacities and latent heats of vaporization. As a result, some cooling devices which release carbon dioxide are more bulky than is commercially acceptable for a portable device.
An alternate procedure for providing a cooling effect in a portable device is to absorb or adsorb the refrigerant vapor in a chamber separate from the chamber in which the evaporation takes place. In such a system, the refrigerant liquid boils under reduced pressure in a sealed chamber and absorbs heat from its surroundings. The vapor generated from the boiling liquid is continuously removed from the first chamber and discharged into a second chamber containing a desiccant or sorbent that absorbs the vapor.
The use of two chambers to produce a cooling effect around one chamber is illustrated in U.S. Pat. No. 4,250,720 to Siegel and Great Britain Patent No. 2,095,386 to Cleghorn, et al. These patents disclose a two-chamber apparatus connected by a tube. The Siegel patent uses water as the refrigerant liquid, while the Cleghorn, et al. patent is not limited to water. The Siegel patent envisions the use of such a cooling device to cool food or beverages.
However, in the Siegel and Cleghorn, et al. patents, the rapid initial cooling effect gradually slows as a result of the both decrease in temperature of the object to be cooled and decrease in the heat transfer area of the first chamber. The decrease in heat transfer area is due to the fact that the portion of the first chamber in contact with the liquid decreases as the liquid vaporizes and the liquid level drops. Moreover, in these systems, the evaporation process is limited by the surface area from which the liquid can boil. In addition, the systems do not effectively minimize the amount of liquid which is entrained in the vapor phase caused by uncontrolled boiling of the evaporating liquid.
Our parent U.S. Pat. No. 4,759,191 discloses a refrigeration system employing a desiccant to absorb the refrigerant vapor. In that refrigeration process, the desiccant evolves heat both from the latent heat of vaporization of the refrigerant and from the chemical reaction heat produced as the liquid condensed from the vapor reacts with the desiccant. Since all desiccants so far found satisfactory for this application deteriorate in their absorptive capabilities as the temperature increases, it is of advantage to refrigeration system compactness to limit the temperature rise of the desiccant to as low a value as possible by removing the chemical reaction heat transferred from the condensed liquid to the dessicant.
Accordingly, one objective of the present invention is to provide a self-contained sorption cooling device with a means to alleviate the decrease in heat transfer as the liquid vaporizes and therefore speed the cooling process.
Another object of the present invention is to accelerate the evaporation process by increasing the surface area from which the liquid can evaporate. As a result, the cooling process will be accelerated as well.
Another object of the present invention is to collect and store heat transferred by the vaporized liquid by the use of a heat sink.
Other objectives will become apparent from the appended drawing and the following Detailed Description of the Invention.